Re: [Patch v3 3/6] cpufreq: qcom-cpufreq-hw: Add dcvs interrupt support

Thara Gopinath
2021-07-09T15:37:24Z

On 7/9/21 2:46 AM, Viresh Kumar wrote:
> On 08-07-21, 08:06, Thara Gopinath wrote:
>> static int qcom_cpufreq_hw_cpu_init(struct cpufreq_policy *policy)
>> {
>> struct platform_device *pdev = cpufreq_get_driver_data();
>> @@ -370,6 +480,10 @@ static int qcom_cpufreq_hw_cpu_init(struct cpufreq_policy *policy)
>> dev_warn(cpu_dev, "failed to enable boost: %d\n", ret);
>> }
>>
>> + ret = qcom_cpufreq_hw_lmh_init(policy, index);
>
> You missed unregistering EM here (which is also missing from exit,
> which you need to fix first in a separate patch).

Hi!

So how exactly do you do this? I checked other users of the api and I do
not see any free. I would say if needed, it should be a separate patch
and outside of this series.

>
>> + if (ret)
>> + goto error;
>> +
>> return 0;
>> error:
>> kfree(data);
>> @@ -389,6 +503,10 @@ static int qcom_cpufreq_hw_cpu_exit(struct cpufreq_policy *policy)
>>
>> dev_pm_opp_remove_all_dynamic(cpu_dev);
>> dev_pm_opp_of_cpumask_remove_table(policy->related_cpus);
>> + if (data->lmh_dcvs_irq > 0) {
>> + devm_free_irq(cpu_dev, data->lmh_dcvs_irq, data);
>
> Why using devm variants here and while requesting the irq ?
>
>> + cancel_delayed_work_sync(&data->lmh_dcvs_poll_work);
>> + }
>
> Please move this to qcom_cpufreq_hw_lmh_exit() or something.

Ok.

>
> Now with sequence of disabling interrupt, etc, I see a potential
> problem.
>
> CPU0 CPU1
>
> qcom_cpufreq_hw_cpu_exit()
> -> devm_free_irq();
> qcom_lmh_dcvs_poll()
> -> qcom_lmh_dcvs_notify()
> -> enable_irq()
>
> -> cancel_delayed_work_sync();
>
>
> What will happen if enable_irq() gets called after freeing the irq ?
> Not sure, but it looks like you will hit this then from manage.c:
>
> WARN(!desc->irq_data.chip, KERN_ERR "enable_irq before
> setup/request_irq: irq %u\n", irq))
>
> ?
>
> You got a chicken n egg problem :)

Yes indeed! But also it is a very rare chicken and egg problem.
The scenario here is that the cpus are busy and running load causing a
thermal overrun and lmh is engaged. At the same time for this issue to
be hit the cpu is trying to exit/disable cpufreq. Calling
cancel_delayed_work_sync first could solve this issue, right ?
cancel_delayed_work_sync guarantees the work not to be pending even if
it requeues itself on return. So once the delayed work is cancelled, the
interrupts can be safely disabled. Thoughts ?

>

--
Warm Regards
Thara (She/Her/Hers)